Running has bone benefits for young women beyond building bone density, according to a study published in the Journal of Clinical Endocrinology and Metabolism.

Researchers used bone density scans to look at what they called "hip geometry"--basically, structural soundness--in 102 women ages 14 to 22. Seventy-nine of the women were athletes who either ran at least 20 miles a week or otherwise tallied at least four hours of weight-bearing activity per week. Some of the athletes were amenorrheic, or without menstrual periods.

Measures of their hips' structural soundness included bone width and "cross-sectional moment of inertia," which is another way of saying the bones' ability to resist bending under pressure.

The researchers found that the women athletes who menstruated had better hip geometry and, not surprisingly, bone mineral density than the amenorrheic athletes and the non-athletic women studied. The amenorrheic athletes, in contrast, were more similar to the non-athletes.

Among the reasons that a young runner might become amenorrheic is simply not eating enough. Here are some fueling tips for avoiding amenorrhea.